The present invention relates to a method for repairing articles made of ceramic composites. In particular, the present invention relates to a method for repairing articles made of fiber-reinforced ceramic composites.
Reinforced ceramic matrix composites (xe2x80x9cCMCsxe2x80x9d) comprising fibers dispersed in continuous ceramic matrices of the same or a different composition are well suited for structural applications because of their toughness, thermal resistance, high-temperature strength, and chemical stability. Such composites typically have high strength-to-weight ratio that renders them attractive in applications in which weight is a concern, such as in aeronautic applications. Their stability at high temperatures renders them very suitable in applications in which the components are in contact with a high-temperature gas, such as in gas turbine engine.
One process for the production of CMCs begins with producing a prepreg tape comprising fibers and a ceramic matrix or matrix precursor material. Fibers, such as ceramic fibers that have been coated with one or more materials to impart certain desired surface properties to them, are impregnated with a suspension comprising powder of the ceramic matrix or matrix precursor material and a temporary binder, and typically wound onto a drum to form the prepreg tape. The prepreg tape is dried and then cut into sections and formed into a fiber preform which is a porous object having a desired shape. The dried prepreg tape is still flexible and can be easily shaped. In another process, the preform is made first using tapes of woven fibers or fibers woven into three-dimensional structures, and fiber coatings are applied by chemical vapor infiltration. The porosity within the fiber preform is then filled with the matrix or matrix precursor material, which in many instances may be a molten metal such as silicon, which eventually produces the finished continuous ceramic matrix surrounding the fibers. SiC fibers have been used as a reinforcing material for ceramics such as SiC, TiC, Si3N4, or Al2O3. The filling of the fiber preform with the matrix precursor material and any attendant reaction between the matrix constituents already in the preform and the precursor material serve to densify the shaped object. This filling or densification may be achieved by chemical-vapor infiltration (xe2x80x9cCVIxe2x80x9d) or liquid-phase infiltration by the matrix precursor material. Liquid-phase infiltration, often by a molten metal, is the preferred method because it is less time consuming and more often produces a fully dense body than the CVI process. Full densification is necessary to achieve good thermal and mechanical properties and, thus, a long-term performance of CMCs.
Polymer infiltration and pyrolysis (xe2x80x9cPIPxe2x80x9d) is another process for the production of CMCs. This process consists of: (1) infiltration of the composite reinforcement preform with one or more organo-metallic polymers, (2) densification or consolidation of the polymer-impregnated reinforcement preform, (3) cure of the polymer matrix to prevent melting during subsequent processing, and (4) pyrolysis and conversion of the cured polymer or polymers into the ceramic matrix. The polymer infiltration of a preform can be accomplished by either solution infiltration or melt infiltration. Ceramic composite matrices, such as SiC, Si3N4, SiON2, BN, AlN, and mixtures thereof, can be prepared from the pyrolysis of respective precursor polymers.
CMCs are quite expensive because their typical production process is rather involved. Therefore, it is desirable to have a method of repairing any CMC pieces, which may be damaged either accidentally or during use, such that they may be salvaged or their useful life may be extended.
A method is provided for repairing an article that comprises a fiber-reinforced ceramic matrix composite (xe2x80x9cCMCxe2x80x9d) material. The CMC comprises fibers embedded in a ceramic matrix material. The method comprises: (a) providing a repairing tape that comprises reinforcement fibers and at least one material selected from the group consisting of a ceramic matrix material, a ceramic matrix precursor material, and mixtures thereof; (b) attaching a portion of the repairing tape to a damaged area of the article; (c) providing an infiltrant phase material comprising at least a material selected from the group consisting of a ceramic matrix material, a ceramic matrix precursor material, and mixtures thereof to the repairing tape portion attached to the damaged area; (d) infiltrating at least the repairing tape portion with the infiltrant phase material to form a repaired area having a fiber-reinforced CMC composition.
In one aspect of the present invention, a portion of the material around the damaged area is removed before a portion of the repairing tape is attached thereto.
In another aspect of the present invention, the portion of the repairing tape attached to the damaged area comprises a plurality of layers of the repairing tape.
Other aspects, advantages, and salient features of the present invention will become apparent from a perusal of the following detailed description, which, when taken in conjunction with the accompanying figures, discloses embodiments of the present invention.